Coconut crab sales from the weekly Friday market in Alofi were monitored over a 3 month
period from 7-9-90 to 14-12-90. Coconut crabs presented for sale at the market were counted
and where possible their TL measured. If a TL measurement was impossible due to the
manner in which the crabs were bound, a weight was taken and then converted to a thoracic
measurement using the following formulas:

Males: TL = 24.628 + 0.02170 × Weight

Females: TL = 18.815 + 0.0462 × Weight

(Formulas generated by conducting a regression analysis on population survey thorax: weight
data.)

During the survey period 12 market days were monitored and a total of 104 individual crabs
and 9 bags of crabs were offered for sale. The majority of crabs available at the market were
male, accounting for 93% of the crabs for which an accurate sex determination was possible.
In fact female crabs were only available at the one market, held on 7-9-90. This corresponds to
the final stages of the coconut crab moulting period and so coconut crab density in the forests
would still be low. Females are generally smaller than males and therefore would fetch lower
sale prices. It is probable that females are only present at the market during the winter months
when insufficient males are available in the forest to meet demand.

The mean TL of market crabs, males in particular, was much higher than that for crabs
recorded during the population surveys. Market male coconut crabs had a mean TL of 48.1
mm (n=97) whereas males from the population surveys had a mean TL of 32.6 mm (n=150).
Obviously there is pronounced size-selection associated with crabs offered for sale at the
market. The extent to which the market size-selection process reflects on actual hunting
size-selection is impossible to determine. While size-selection is prominent amongst hunters,
small crabs are not ignored and will be taken provided the effort in catching them is no greater
than that required for large crabs.

During this author's visit to Niue in July 1991 a survey was conducted of crabs offered for
sale from the Friday (19-7-91) Alofi market. A total of 54 crabs, all males, were recorded with
a mean TL of 43.9 mm. This value is significantly less (T-test, p=0.001) than the mean TL
recorded for market sales of male crabs during a similar month in 1990. This suggests that
there has been a reduction in availability and/or size of the large male crabs in the coconut
crab population on Niue; the result of high and size-selective hunting pressure.